Modular, zone-specific medical electrical lead design

ABSTRACT

A medical electrical lead configured to be coupled to a pulse generator in a cardiac rhythm management system. The lead comprises a proximal terminal connector configured for coupling the lead to the pulse generator, and a plurality of longitudinally arranged lead segments each configured to exhibit one or more predetermined physical characteristics based on the implantation location for the respective segment. The lead segments may be pre-fabricated as separate modules optimized for the operating environment and/or delivery requirements of the respective segments. The pre-fabricated modules are longitudinally arranged and joined to form the lead.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/371,268, filed Feb. 13, 2009, now patented as U.S. Pat. No,7,946,980, which claims the benefit under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/028,961, filed Feb. 15, 2008,entitled “MODULAR, ZONE-SPECIFIC MEDICAL ELECTRICAL LEAD DESIGN,” whichare incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to medical electrical leads for use incardiac rhythm management systems, and in particular, to medicalelectrical leads configured for partial implantation in a heart of apatient.

BACKGROUND

Various types of medical electrical leads for use in cardiac rhythmmanagement systems are known. Such leads typically extendintravascularly to an implantation location within or on a patient'sheart, and thereafter coupled to a pulse generator or other implantabledevice for sensing cardiac electrical activity, delivering therapeuticstimuli, and the like. The leads are desirably highly flexible toaccommodate natural patient movement, yet also constructed to haveminimized profiles. At the same time, the leads are exposed to variousexternal forces imposed, for example, by the human muscular and skeletalsystem, the pulse generator, other leads, and surgical instruments usedduring implantation and explantation procedures. There is a continuingneed for improved lead designs.

SUMMARY

The present invention, in one embodiment, is a method of making animplantable medical electrical lead. The method comprises providing aplurality of pre-fabricated lead modules each corresponding to a leadsegment configured for a predetermined implantation site, includingproviding a first module defining to a first proximal lead segment,providing a second module defining to a second proximal lead segment,providing a third module defining to an electrode lead segment, andproviding a fourth module defining to a distal fixation segmentincluding a fixation helix. The method further comprises longitudinallyassembling and joining the first, second, third and fourth modules.

In another embodiment, the present invention is a method of making animplantable medical electrical lead adapted to be at least partiallyimplanted in a heart of a patient and to be coupled to a pulse generatorof a cardiac rhythm management system. The method comprises configuringeach of a plurality of pre-fabricated lead segments to exhibit one ormore desired physical characteristics depending on an implantationlocation of the respective segment. The lead segments include at leastone segment configured for subcutaneous implantation and to exhibit oneor more of a greater stiffness, crush resistance, cut resistance, ortemperature resistance than each of the other of the plurality ofsegments. The lead segments further include at least one segmentconfigured for intravascular implantation and to exhibit one or more ofa greater flexibility and smaller outside diameter than the at least onesegment configured for subcutaneous implantation, and at least onesegment configured for intracardiac implantation and to exhibit one ormore of a greater flexibility and smaller outside diameter than the atleast one segment configured for subcutaneous implantation. The methodfurther includes longitudinally arranging and coupling the leadsegments.

In yet another embodiment, the present invention is a medical electricallead configured to be coupled to a pulse generator in a cardiac rhythmmanagement system. The lead comprises a proximal terminal connectorconfigured for coupling the lead to the pulse generator, and a pluralityof longitudinally arranged pre-fabricated lead segments. Thepre-fabricated lead segments include a first proximal segment coupledthe terminal connector, a second proximal segment coupled to andextending distally from the first proximal segment, an electrode segmentcoupled to and extending distally from the second proximal segment andincluding an electrode configured to be electrically coupled to thepulse generator to deliver an electrical stimulus to a patient, and adistal fixation segment coupled to and extending distally from thedistal electrode segment and configured to secure the lead to thecardiac tissue. Each segment is coupled to an adjacent segment by ajoint.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cardiac rhythm management (CRM) systemincluding a pulse generator and a plurality of leads according to anembodiment of the present invention.

FIG. 2A is an isometric illustration of one of the leads of FIG. 1according to one embodiment of the present invention.

FIGS. 2B and 2C are enlarged longitudinal and transverse cross-sectionalviews of a portion the lead of FIG. 2A taken along the lines 2B-2B and2C-2C, respectively, in FIG. 2A.

FIG. 3A is an isometric illustration of an alternative lead for use withthe CRM system of FIG. 1 according to one embodiment of the presentinvention.

FIG. 3B is an enlarged transverse cross-sectional view of a portion thelead of FIG. 3A taken along the lines 3B-3B.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of a cardiac rhythm management (CRM) system10 according to an embodiment of the present invention. As shown in FIG.1, the CRM system 10 includes a pulse generator 12 coupled to aplurality of leads 14, 16 deployed in a patient's heart 18. As furthershown in FIG. 1, the heart 18 includes a right atrium 24 and a rightventricle 26 separated by a tricuspid valve 28. During normal operationof the heart 18, deoxygenated blood is fed into the right atrium 24through the superior vena cava 30 and the inferior vena cava 32. Themajor veins supplying blood to the superior vena cava 30 include theright and left axillary veins 34 and 36, which flow into the right andleft subclavian veins 38 and 40. The right and left external jugular 42and 44, along with the right and left internal jugular 46 and 48, jointhe right and left subclavian veins 38 and 40 to form the right and leftbrachiocephalic veins 50 and 52, which in turn combine to flow into thesuperior vena cava 30.

The leads 14, 16 operate to convey electrical signals and stimulibetween the heart 18 and the pulse generator 12. In the illustratedembodiment, the lead 14 is implanted in the right ventricle 26, and thelead 16 is implanted in the right atrium 24. In other embodiments, theCRM system 10 may include additional leads, e.g., a lead extending intoa coronary vein for stimulating the left ventricle in a bi-ventricularpacing or cardiac resynchronization therapy system. As shown, the leads14, 16 enter the vascular system through a vascular entry site 54 formedwall of the left subclavian vein 40, extend through the leftbrachiocephalic vein 52 and the superior vena cava 30, and are implantedin the right ventricle 26 and right atrium 24, respectively. In otherembodiments, the leads 14, 16 may enter the vascular system through theright subclavian vein, the left axillary vein 36, the left externaljugular 44, the left internal jugular 48, the left brachiocephalic vein52, or other suitable vascular access locations.

The pulse generator 12 is typically implanted subcutaneously within animplantation location or pocket in the patient's chest or abdomen. Thepulse generator 12 may be any implantable medical device known in theart or later developed for delivering an electrical therapeutic stimulusto the patient. In various embodiments, the pulse generator 12 is apacemaker, an implantable cardiac defibrillator, and/or includes bothpacing and defibrillation capabilities. The portions of the leads 14, 16extending from the pulse generator 12 to the vascular entry site 54 arealso located subcutaneously or submuscularly. Any excess lead length,i.e., length beyond that needed to reach from the pulse generator 12location to the desired intracardiac implantation site, is generallycoiled up in the subcutaneous pocket near the pulse generator 12.

FIG. 2A is an isometric illustration of the lead 14 according to oneembodiment of the present invention. As shown in FIG. 2A, the lead 14includes, in one embodiment, a connector 70, a proximal portion 76, anda distal portion 84. As further shown, the proximal portion 76 iscoupled to and extends distally from the connector 70, and the distalportion 84 is coupled to and extends distally from the proximal portion76. The connector 70 is configured to mechanically and electricallycouple the lead 14 to a header on the pulse generator 12. In variousembodiments, the proximal portion 76 is dimensioned to extend from theimplanted pulse generator 12 and into the vascular system. Thus, part ofthe proximal portion 76 is located generally subcutaneously when thelead 14 is implanted, with the remaining part extending intravascularly,i.e., from just distal to the vascular entry site 54, through the leftsubclavian vein 40 and the left brachiocephalic vein 52. The distalportion 84 is dimensioned to extend from the proximal portion 76,through the superior vena cava 30 and right atrium 24 to a location inthe right ventricle 26.

As shown, the proximal and distal portions 76, 84 are each formed from aplurality of longitudinally-arranged lead segments. Thus, in theillustrated embodiment, the proximal portion 76 includes a firstproximal segment 94 and a second proximal segment 98 coupled to andextending distally from the first proximal segment 94. Additionally, thedistal portion 84 includes an electrode segment 106 and a distalfixation segment 112. As further shown, the respective adjacent segmentsare coupled together at joints 113, 114, and 115.

In the illustrated embodiment, the electrode segment 106 includes aflexible coil electrode 120 operable as a shocking electrode forproviding a defibrillation shock to the heart 18. The coil electrode 120can be of any configuration suitable for implantable defibrillationleads, whether now known or later developed. In one embodiment, the coilelectrode 120 includes a coating configured to control (i.e., promote ordiscourage) tissue in-growth. In one embodiment, the electrode 120 iscoated with an expanded polytetrafluoroethylene (ePTFE) coatingconfigured to permit intimate fluid contact between the electrode 120and the cardiac tissue and also to substantially prevent tissue ingrowthand fibrosis that could otherwise adhere to the electrode surfaces. Inone embodiment, the coil electrode 120 is uncoated.

As further shown, the distal fixation segment 112 includes a distal tip130 from which an extendable/retractable fixation helix 136 can beextended to penetrate the cardiac tissue to secure the distal tip 130 ofthe lead 14 thereto. In such embodiments, the fixation helix 136 ismechanically coupled to a mechanism, e.g., a rotatable terminal pin ofthe terminal connector 70 operable by the implanting physician to extendand retract the helix 136 as necessary. In other embodiments, thefixation helix 136 is a fixed helix (i.e., not extendable/retractable)and may be covered by a dissolvable material to prevent the helix 136from catching on body tissue during delivery to the implantation site.In still other embodiments, other fixation means, e.g., tines,pre-formed and pre-biased lead portions, stents, etc. are employed. Invarious embodiments, the fixation helix 136 is also configured as apace/sense electrode, and thus is electrically coupled to the pulsegenerator 12 via the connector 70 (see FIG. 1). In various otherembodiments, other electrode configurations may be employed depending onthe particular therapeutic needs of the patient.

FIGS. 2B and 2C are longitudinal and transverse cross-sectional views ofa portion of the lead 14 taken along the lines 2B-2B and 2C-2C,respectively, in FIG. 2A. As shown, the lead 14 includes a main bodymember 140, a reinforcing layer 150, a coil conductor 156, and a cableconductor 160. As shown, the body member 140 includes a pair oflongitudinal lumens 166, 172 in which the coil and cable conductors 156,160 reside.

In various embodiments, the coil conductor 156 is mechanically andelectrically coupled to the fixation helix 136 and to the terminalconnector 70. Thus, as will be appreciated, the coil conductor 156operates to convey electrical signals between the fixation helix 136 andthe connector 70, and thus also to the pulse generator 12. The coilconductor 156 also operates to transmit torque applied at the connector70 (e.g., via a rotatable terminal pin) to the fixation helix 136 forextending and retracting the fixation helix 136 as required. The cableconductor 160 is mechanically and electrically coupled to the coilelectrode 120, and thus operates to convey electrical signals betweenthe coil electrode 120 and the connector 70 and pulse generator 12.

As shown, the lead body member 140 extends longitudinally from theconnector 70 to the distal fixation segment 112, and through the coilelectrode 120. As further shown, in the illustrated embodiment, the leadbody member 140 is circumferentially covered by the reinforcing layer150 in the first proximal segment 94.

Any conventional or later developed materials suitable for medicalelectrical lead construction can be used to construct the lead 14. Forexample, the lead body member 140 can be made from any flexible,biocompatible materials suitable for lead construction. In variousembodiments, the lead body member 140 is made from a flexible,electrically insulative material such as silicone rubber. Similarly, theconnector 70, the coil and cable conductors 156, 160, the coil electrode120, the fixation helix 136, and the corresponding extension/retractionmechanism (not shown), if present, may be made from any conventional orlater developed materials suitable for such uses.

In the various embodiments of the present invention, the respective leadsegments are each configured for implantation in a different region ofthe patient's body, and accordingly, are configured to exhibit specificphysical and functional characteristics depending on the respectiveimplantation locations. In one embodiment, the first proximal segment isconfigured to be implanted substantially subcutaneously, i.e., in the“pocket” region in which the pulse generator 12 is also implanted, whilethe second proximal segment 98 is configured to be implanted primarilyintravascularly, e.g., within the left subclavian vein 40 and the leftbrachiocephalic vein 52 and into the superior vena cava 30 (see FIG. 1).Additionally, the electrode segment 106 and the fixation segment 112 areconfigured to be implanted within the right atrium 26 and/or rightventricle 24, and are thus configured for intracardiac implantation.

Because the various lead segments described above are configured tooccupy different implantation locations, the respective segments arelikely to be subject to different operating and delivery conditions.According to various embodiments of the present invention, the varioussegments are therefore configured differently to optimize theperformance of the lead in light of these differing operatingenvironments and delivery conditions. Additionally, in variousembodiments, the respective lead segments are pre-fabricated as separatemodules and assembled to form the lead 14.

For example, the subcutaneously implanted first proximal segment 94 may,in various circumstances, be subject to abrasion and crushing loadsimparted by interaction of the lead 14 with other leads, the pulsegenerator 12, and/or the skeletal and muscular systems of the patientitself. Additionally, suture sleeves may be disposed about the lead 14in the subcutaneous first proximal segment 94 to secure the lead 14 tothe adjacent fascial tissue. As will be appreciated, use of sutures tosecure the lead 14 to the tissue imparts a compressive force on the lead14.

The subcutaneous first proximal segment 94 may also be subjected todamage (e.g., cutting, burning, etc.) by various surgical instruments.For example, an electrocautery instrument or mechanical cuttinginstrument (e.g., a scalpel) may be used to cut fibrosed tissue awayfrom the bodies of implanted leads to allow such leads to be removedand/or replaced as necessary. In such circumstances, the electrocauteryinstrument or scalpel may inadvertently damage the insulative coveringof an adjacent lead that is not otherwise intended to be removed. Inthis regard, in some embodiments, it may be desirable to configure thefirst proximal segment 94 to resist fibrotic tissue encapsulation in thefirst instance.

Additionally, in some circumstances, the proximal portion 76 of the leadmay advantageously be made relatively stiff compared to the distalportion 84 so as to enhance the pushability and/or torqueability of thelead 14 during delivery.

At the same time, however, the intravascularly implanted second proximalsegment 98 may, in various applications, not be subjected to externalforces and loads comparable to those imposed on the subcutaneous firstproximal segment 94. In contrast, the second proximal segment 98 isadvantageously made highly flexible to accommodate natural cardiacmotion, and is also configured to have a minimum profile in light of therelatively confined spaces in which it is implanted. Similarly,different operating and use considerations apply to the electrode anddistal fixation segments 106, 112 as compared to the subcutaneouslyimplanted first proximal segment 94.

Accordingly, in various embodiments of the present invention, the leadsegments are each specifically designed and optimized based on theirrespective operating environments and/or desired functionality. Forexample, in various embodiments, the subcutaneously implanted firstproximal segment 94 is optimized to have enhanced fatigue properties andfor enhanced resistance to damage from cutting, high temperatures (e.g.,electrocautery), crushing, and/or fibrotic encapsulation.

In the illustrated embodiment, the first proximal segment 94 includesthe reinforcing layer 150 to enhance the abrasion, crush, temperature,and/or cut resistance as well as stiffness of this portion of the lead.In one embodiment, the reinforcing layer 150 is also configured tosubstantially prevent tissue ingrowth and fibrotic tissue encapsulation.

In some embodiments, the reinforcing layer 150 is configured as anarmoring layer such as is described in co-pending and commonly assignedU.S. Provisional Patent Application No. 61/028,999 to Reddy filed onFeb. 15, 2008 and titled “Medical Electrical Lead with ProximalArmoring” and U.S. patent application Ser. No. 12/371,264, to Reddyfiled on same date as the present application and titled “MedicalElectrical Lead with Proximal Armoring,” both of which is incorporatedherein by reference in their entirety. In one embodiment, thereinforcing layer 150 includes a lubricious, flexible ribbon ofpolymeric material, e.g., polytetrafluoroethylene (PTFE) or expandedpolytetrafluoroethylene (ePTFE) disposed over the lead body 70.

In various other embodiments, the lead body member 140 in the firstproximal segment 94 includes a reinforcing braid, wire, mesh, or otherfunctionally comparable structure in lieu of or in addition to thereinforcing layer 150 to enhance the desired physical characteristics ofthe first proximal segment 94. In other embodiments, however, the leadoptimization is accomplished by material selection, e.g., by making thelead body member 140 out of a highly lubricious and/or relatively stiffpolymer, materials that are resistant to electrocautery damage (e.g.,ePTFE), and the like.

The remaining segments of the lead 14 are also specifically tailored andoptimized for their own operating environments. In various embodiments,the intravascularly implanted second proximal segment 98 is configuredto provide one or more of a minimized profile (e.g., outer diameter),high flexibility, and/or resistance to tissue adhesion and attachment tothe venous walls.

Similarly, in various embodiments, the electrode segment 106 isoptimized for enhanced electrical performance, reduced size, fatigueresistance, high flexibility, and to prevent tissue ingrowth. In variousembodiments, the electrode segment 106 includes a pre-formed bias so asto tend to urge the electrode 120 into the cardiac tissue whenimplanted. Optimization of the distal fixation segment 112 includes,without limitation, configuring this segment to promote tissue ingrowthfor enhanced fixation and stability, enhanced electrical performance(i.e., when the fixation helix 136 is also operative as a pace/senseelectrode), and/or to be substantially atraumatic. In some embodiments,the distal fixation segment 112 is also pre-curved, e.g., in a J-shape,to urge the fixation helix 136 to a desired position in the heart 18. Ofcourse, the foregoing examples are illustrative only, and in no waylimiting.

The means for optimizing the respective lead segments are not limited,and can be accomplished by the inclusion or omission of additionalstructure (e.g., the reinforcing layer 150), by selecting materialshaving the desired properties, varying dimensions of the varioussegments, and the like. In various embodiments, for example, theoptimization features are incorporated into the lead body member 140,the coil and/or cable conductors 156, 160, the electrode 120, or any ofthe above. Again, the various embodiments of the present inventionencompass any suitable means for optimization of the respective leadbody segments for their specific service conditions.

As discussed above, the first and second proximal lead segments 94, 98,the electrode segment 106, and the distal fixation segment 112 areadvantageously pre-fabricated as separate modules and subsequentlyassembled and joined to form the completed lead 14. For example, in onembodiment, the proximal fixation segment 94 includes, in predeterminedlengths, a section of the lead body member 140, the outer tubing 146,the reinforcing layer 150, and the coil and cable conductors 156, 160.Similarly, the second proximal segment 98 includes a section of the leadbody member 140, and the coil and cable conductors 156, 160. Theelectrode segment 106 can in turn be pre-assembled to include anadditional section of the lead body member 140, the coil and cableconductor 156, 160, and the coil electrode 120. Finally, the distalfixation segment 112 is pre-fabricated to include the fixationhelix/electrode 136 and the associated internal mechanisms forfacilitating extension and retraction of the helix 136.

To form the lead 14, the respective pre-fabricated modules are assembledand joined longitudinally. For example, the conductor sections foradjacent segments are electrically and mechanically connected via asuitable joining process, e.g., crimping, welding, and the like. Invarious embodiments, crimp tubes or comparable structures known in theart are included on the modules to facilitate coupling the conductorsections in the adjacent lead segments. Similarly, the sections of thelead body member 140 in adjacent lead segments are joined via a suitableprocess for joining polymeric materials, e.g., using medical adhesive,shrink tubing, and the like. Additionally, the sections of the lead bodymember 140 in the respective lead segments may include windows throughtheir outer surfaces near the ends of the segments, or similar featuresto provide access for facilitating coupling the conductor sections ofthe adjacent segments.

In various embodiments, one or more of the pre-fabricated lead modulesmay not include any or all of the conductor sections, thus avoidingmultiple conductor joints along the length of the lead 14. For example,in one embodiment, the first and second proximal lead segments 94, 98,the electrode segment 106, and the distal fixation segment 112 do notinclude sections of the coil and cable conductors 156, 160, so thatthese conductors can be provided in uninterrupted lengths. Thus, thelead 14 could be assembled by coupling the conductors 156, 160 torespective electrical contacts on the connector 70, and then sliding thefirst and second proximal lead segments 94, 98, the electrode segment106, and the distal fixation segment 112 over the conductors 156, 160.The required mechanical and electrical connections are made between thecoil conductor 156 and the fixation helix 136, and also between thecable conductor 160 and the coil electrode 120, using any suitablejoining technique, e.g., crimping, welding, and the like. The polymericlead body sections are then spliced and joined using a suitable polymerjoining technique, e.g., medical adhesive, shrink-tubing, and the like.

The pre-fabricated modular construction of the segmented lead 14 hasnumerous advantages. For example, the respective lead segment modulescan be mass produced in various lengths, diameters, and/or to conform toother specific specifications (e.g., crush or abrasion resistance, hightemperature compatibility for electrocautery damage resistance,flexibility, and the like). These modules can then be combined to createwide ranges of lead configurations. Assembly of the pre-fabricatedmodules also advantageously provides manufacturing efficiencies in somecircumstances. For example, providing one or more modules with conductor(coil and/or cable) segments which are subsequently joined to theconductors of adjacent modules can eliminate the need to stringelongated conductors through the entire length of the lead as is thecase in conventional lead designs. Other advantages of the modular,segmented leads of the various embodiments of the present invention willbecome apparent based on the foregoing.

Although the embodiments illustrated above include a single coildefibrillation electrode 120, other embodiments have differentconfigurations. FIG. 3A is an isometric illustration of an alternativelead 214 for use with the CRM system of FIG. 1, and FIG. 3B is atransverse cross-sectional view of a portion of the lead 214 taken alongthe line 3B-3B in FIG. 3A, according to an embodiment of the presentinvention. As shown, the lead 214 includes a connector 270, a proximalportion 276, and a distal portion 284. As further shown, the proximalportion 276 is coupled to and extends distally from the connector 270,and the distal portion 284 is coupled to and extends distally from theproximal portion 276. The connector 270 is configured to mechanicallyand electrically couple the lead 214 to a header on the pulse generator12.

Like the corresponding elements of the lead 14 described above, theproximal portion 276 is dimensioned to extend from the implanted pulsegenerator 12 and into the vascular system, e.g., into the leftsubclavian vein 40 (see FIG. 1), to the superior vena cava 30.Similarly, the distal portion 284 is dimensioned to extend from theproximal portion 276, through the superior vena cava 30 and right atrium24 to a location in the right ventricle 26.

As with the lead 14 above, the proximal and distal portions 276, 284 areeach formed of a plurality of longitudinally-arranged lead segments.Thus, in the illustrated embodiment, the proximal portion 276 includes afirst proximal segment 294 and a second proximal segment 298 coupled toand extending distally from the first proximal segment 294.Additionally, as further shown, the distal portion 284 includes anelectrode segment 306 and a distal fixation segment 312.

In the illustrated embodiment, the electrode segment 306 includes aproximal coil electrode 318, a distal coil electrode 324, and a spacerportion 330 therebetween. The proximal coil electrode 318 is coupled toand extends distally from the second proximal segment 298, and thedistal fixation segment 312 is coupled to and extends distally from thedistal coil electrode 324. Thus, the lead 214 operates as a multi-polardefibrillation lead. As further shown, the distal fixation segment 312includes a fixation helix 336.

As shown in the cross-sectional view of FIG. 3B, the lead 214 includes amain body member 340, a reinforcing layer 350, a coil conductor 356, anda pair of cable conductors 360, 362. As shown, the body member 340includes a coil conductor lumen 366 in which the coil conductor 356resides, and further includes a pair of cable conductor lumens 372, 374in which the cable conductors 360, 362 reside.

In various embodiments, the coil conductor 356 is mechanically andelectrically coupled to the fixation helix 336 and to the terminalconnector 270, and operates in much the same or identical manner as thecoil conductor 150 of the lead 14. Similarly, each of the cableconductors 360, 362 is mechanically and electrically coupled to one ofthe coil electrodes 318, 324, and thus operates to convey electricalsignals between the respective coil electrode and the connector 270 andpulse generator 12. With the exception of the additional cable conductorand corresponding lumen in the lead 214, the first and second proximalsegments 294, 298 and the distal fixation segment 312 operate and areconfigured, in various embodiments, in substantially the same or anidentical manner as the corresponding elements of the lead 14 describedabove, and thus are not describe in further detail here.

The segments of the lead 214 are also specifically designed andconfigured so as to provide optimal performance for their respectiveoperating environments and/or delivery conditions. Thus, in variousembodiments, the first and second proximal segments 294, 298, theelectrode segment 306, and the distal fixation segment 312 areconfigured in much the same or an identical manner as the correspondingsegments of the lead 14. Additionally, the spacer portion 330 of theelectrode segment 306 is configured, in various embodiments, for optimalsize (typically being relatively small in diameter), high flexibility,and fatigue performance due to the natural movement of the patient'sheart.

As with the lead 14, the respective segments of the lead 214 are, invarious embodiments, pre-fabricated as separate modules and subsequentlyassembled and joined to form the completed lead 214. In one embodiment,the electrode segment 306 is a single module including the proximal anddistal electrodes 318, 324 and the spacer portion 330, as well ascorresponding sections of the main body member 340, the outer tubing346, the coil conductor 356, and the cable conductors 360, 362. In oneembodiment, each of the coil electrodes 318, 324 and the spacer portion330 are pre-fabricated as a separate module (including correspondingbody, outer tubing, and conductor sections). In one embodiment, thespacer portion 330 is pre-fabricated along with one of the electrodes318 or 324 as a single module. In any case, the respective modules aresubsequently assembled and joined in the manner described above withrespect to the lead 14.

Although the leads 14, 214 described above are both defibrillation leadsincluding coil shocking electrodes adapted for intracardiacimplantation, it will be appreciated that the zone-specific, modularlead construction concepts described herein can also be utilized for anyimplantable lead configurations, whether now known or later developed.For example, in other defibrillation lead embodiments, the shockingelectrodes can take on any other suitable form, e.g., conductive braids,meshes, rings, conductive polymers, and the like. Additionally, variousother embodiments of the present invention include right atrial and/orright ventricular pace/sense leads, epicardial pacing and/ordefibrillation leads, coronary venous leads configured to be implantedin the coronary veins for left ventricular stimulation, and the like. Aswill be appreciated, the coil defibrillation electrodes, e.g., theelectrode 120, are omitted from such leads. Rather, such leads mayinclude smaller ring or similar electrodes on the lead bodies, tipelectrodes, and/or pad electrodes, as are known in the art. In variousembodiments, the foregoing pacing leads can be unipolar, or multipolarand can include any suitable conductor configuration, e.g., single ormuli-filar coil conductors (coaxial or co-radial design), cableconductors, conductive ribbons, solid wires, and the like. In oneembodiment, for example, the lead is a unipolar pacing lead configuredfor either right atrial, right ventricular, or coronary venousimplantation, and includes only a single tip electrode or ring electrodenear its distal end.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

1. A method of making an implantable medical electrical lead, the methodcomprising: providing a plurality of pre-fabricated lead modules eachcorresponding to a lead segment configured for a predeterminedimplantation site, including: providing a first module corresponding toa first proximal lead segment; providing a second module correspondingto a second proximal lead segment; providing a third modulecorresponding to an electrode lead segment; and providing a fourthmodule corresponding to a distal fixation sement; configuring each ofthe modules to exhibit one or more physical characteristics depending onthe implantation location of the corresponding segment; andlongitudinally assembling and joining the first, second, third, andfourth modules; wherein the first proximal lead segment is configured tobe implanted subcutaneously, the second proximal segment is configuredto be implanted intravascularly, and the electrode and distal fixationsegments are configured to be implanted in a cardiac chamber.
 2. Themethod of claim 1, wherein assembling and joining the lead modulesincludes joining the first module to the second module, the secondmodule to the third module, and the third module to the fourth module.3. The method of 1, wherein configuring each of the modules includes:configuring the first module to exhibit one or more of an enhanced cutresistance, an enhanced crush resistance, an enhanced high temperatureresistance, or an enhanced resistance to fibrotic encapsulation,relative to the second, third, or fourth modules.
 4. The method of claim3, wherein configuring each of the modules includes: configuring thesecond and the third modules to have a smaller outside diameter and agreater flexibility than the first module.
 5. The method of claim 4,wherein configuring each of the modules includes configuring the fourthmodule to promote tissue ingrowth.
 6. The method of claim 5, wherein:providing the first and second modules includes: providing first andsecond lead modules each including a lead body member segment having afirst and second longitudinal lumen therethrough; a first conductorsection extending at least partially within the first lumen; and asecond conductor extending at least partially within the second lumen;and assembling and joining the modules includes: joining the firstconductor section of the first module to the first conductor section ofthe second module; joining the second conductor section of the firstmodule to the second conductor section of the second module; and joiningthe lead body member sections of the first and second modules.
 7. Themethod of claim 1, wherein providing the third module includes providinga third module including a proximal electrode, a distal electrode, and aspacer portion therebetween.
 8. The method of claim 7, wherein thedistal fixation segment includes a fixation helix that is configured todeliver a pacing stimulus to the heart.
 9. The method of claim 8,wherein providing the plurality of lead modules includes: providing afirst module configured to exhibit one or more of an enhanced cutresistance, an enhanced crush resistance, an enhanced high temperatureresistance, or an enhanced resistance to fibrotic encapsulation,relative to the second, third, or fourth modules; and providing asecond, third, and fourth module each configured to exhibit a greaterflexibility and a smaller outside diameter than the first module.
 10. Amethod of making an implantable medical electrical lead adapted to be atleast partially implanted in a heart of a patient and to be coupled to apulse generator of a cardiac rhythm management system, the methodcomprising: configuring each of a plurality of pre-fabricated leadsegments to exhibit one or more desired physical characteristicsdepending on an implantation location of the respective segment, thelead segments including: at least one segment configured forsubcutaneous implantation; at least one segment configured forintravascular implantation; and at least one segment configured forintracardiac implantation; and longitudinally arranging and coupling thelead segments; wherein the at least one segment configured forsubcutaneous implantation exhibits one or more of a greater stiffness,crush resistance, cut resistance, or temperature resistance than each ofthe other of the plurality of segments.
 11. A method of making animplantable medical electrical lead adapted to be at least partiallyimplanted in a heart of a patient and to be coupled to a pulse generatorof a cardiac rhythm management system, the method comprising:configuring each of a plurality of pre-fabricated lead segments toexhibit one or more desired physical characteristics depending on animplantation location of the respective segment, the lead segmentsincluding: at least one segment configured for subcutaneousimplantation; at least one segment configured for intravascularimplantation; and at least one segment configured for intracardiacimplantation; and longitudinally arranging and coupling the leadsegments; wherein the at least one segment configured for intravascularimplantation or the at least one segment configured for intracardiacimplantation exhibits one or more of a greater flexibility and smalleroutside diameter than the at least one segment configured forsubcutaneous implantation.
 12. A method of making an implantable medicalelectrical lead adapted to be at least partially implanted in a heart ofa patient and to be coupled to a pulse generator of a cardiac rhythmmanagement system, the method comprising: configuring each of aplurality of pre-fabricated lead segments to exhibit one or more desiredphysical characteristics depending on an implantation location of therespective segment, the lead segments including: at least one segmentconfigured for subcutaneous implantation; at least one segmentconfigured for intravascular implantation; and at least one segmentconfigured for intracardiac implantation; and longitudinally arrangingand coupling the lead segments; wherein the at least one segmentconfigured for intracardiac implantation includes: an electrode segmentincluding at least a first electrode configured to deliver an electricalstimulus to the heart; and a distal fixation segment including afixation helix configured to penetrate tissue of the heart to secure thelead thereto and further configured as a second electrode configured todeliver an electrical stimulus to the heart.
 13. A method of making animplantable medical electrical lead adapted to be at least partiallyimplanted in a heart of a patient and to be coupled to a pulse generatorof a cardiac rhythm management system, the method comprising:configuring each of a plurality of pre-fabricated lead segments toexhibit one or more desired physical characteristics depending on animplantation location of the respective segment, the lead segmentsincluding: at least one segment configured for subcutaneousimplantation; at least one segment configured for intravascularimplantation: and at least one segment configured for intracardiacimplantation; and longitudinally arranging and coupling the leadsegments; wherein the at least one segment configured for intracardiacimplantation includes an electrode located at or near a distal tip ofthe lead, the electrode configured to deliver a pacing stimulus to theheart.
 14. A method of making an implantable medical electrical leadadapted to be at least partially implanted in a heart of a patient andto be coupled to a pulse generator of a cardiac rhythm managementsystem, the method comprising: configuring each of a plurality ofpre-fabricated lead segments to exhibit one or more desired physicalcharacteristics depending on an implantation location of the respectivesegment, the lead segments including: at least one segment configuredfor subcutaneous implantation; at least one segment configured forintravascular implantation; and at least one segment configured forintracardiac implantation; and longitudinally arranging and coupling thelead segments; wherein the at least one segment configured forsubcutaneous implantation includes a reinforcing structure.